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<H2>
LAMMPS Units</H2>
<P>
<A HREF="README.html">Return</A> to top-level LAMMPS documentation.</P>
<P>
This file describes the units associated with many of the key variables 
and equations used inside the LAMMPS code. Units used for input command 
parameters are described in the input_commands file. The input command 
&quot;units&quot; selects between conventional and Lennard-Jones units. 
See the force_fields file for more information on units for the force 
field parameters that are input from data files or input scripts. </P>
<P>
Conventional units: </P>
<UL>
    <LI>
    distance = Angstroms 
    <LI>
    time = femtoseconds 
    <LI>
    mass = grams/mole 
    <LI>
    temperature = degrees K 
    <LI>
    pressure = atmospheres 
    <LI>
    energy = Kcal/mole 
    <LI>
    velocity = Angstroms/femtosecond 
    <LI>
    force = grams/mole * Angstroms/femtosecond^2 
    <LI>
    charge = +/- 1.0 is proton/electron
</UL>
<P>
LJ reduced units: </P>
<UL>
    <LI>
    distance = sigmas 
    <LI>
    time = reduced LJ tau 
    <LI>
    mass = ratio to unitless 1.0
    <LI>
    temperature = reduced LJ temp 
    <LI>
    pressure = reduced LJ pressure 
    <LI>
    energy = epsilons 
    <LI>
    velocity = sigmas/tau 
    <LI>
    force = reduced LJ force (sigmas/tau^2) 
    <LI>
    charge = ratio to unitless 1.0
</UL>
<HR>
<P>
This listing of variables assumes conventional units; to convert to LJ 
reduced units, simply substitute the appropriate term from the list 
above. E.g. x is in sigmas in LJ units. Per-mole in any of the units 
simply means for 6.023 x 10^23 atoms.</P>
<P>
</P>
<PRE>
Meaning        Variable        Units

positions      x               Angstroms
velocities     v               Angstroms / click (see below)
forces         f               Kcal / (mole - Angstrom)                
masses         mass            gram / mole
charges        q               electron units (-1 for an electron)
                                 (1 e.u. = 1.602 x 10^-19 coul)

time           ---             clicks (1 click = 48.88821 fmsec)
timestep       dt              clicks
input timestep dt_in           fmsec
time convert   dtfactor        48.88821 fmsec / click

temperature     t_current       degrees K
                t_start
                t_stop
input damping   t_freq_in       inverse fmsec
internal temp   t_freq          inverse clicks
  damping

dielec const    dielectric      1.0 (unitless)
Boltmann const  boltz           0.001987191 Kcal / (mole - degree K)

virial          virial[xyz]     Kcal/mole = r dot F
pressure factor pfactor         68589.796 (convert internal to atmospheres)
internal        p_current       Kcal / (mole - Angs^3)
  pressure      p_start
                p_stop
input press     p_start_in      atmospheres
                p_stop_in
output press    log file        atmospheres
input damping   p_freq_in       inverse time
internal press  p_freq          inverse clicks
  damping

pot eng         e_potential     Kcal/mole
kin eng         e_kinetic       Kcal/mole
eng convert     efactor         332.0636 (Kcal - Ang) / (q^2 - mole)
                                (convert Coulomb eng to Kcal/mole)

LJ coeffs       lja,ljb         Kcal-Angs^(6,12)/mole

bond            various         see force_fields file
  parameters    2,3,4-body
                terms
</PRE>
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